Engine feedback control system and method

ABSTRACT

This disclosure provides a system and method for controlling internal combustion engine system to reduce operation variations among plural engines. The system and method utilizes single-input-single-output (SISO) control in which a single operating parameter lever is selected from among exhaust gas recirculation (EGR) fraction and charge air mass flow (MCF), and a stored reference value associated with the selected lever is adjusted for an operating point in accordance with a difference between a measured emissions characteristic and a pre-calibrated reference value of the emissions characteristic for that operating point. Adjusting the selected operating parameter lever towards the theoretical pre-calibrated reference value of the operating parameter lever for each of plural operating points can reduce engine-to-engine variations in engine out emissions.

This application is a continuation of U.S. patent application Ser. No.13/656,308, filed Oct. 19, 2012, entitled “ENGINE FEEDBACK CONTROLSYSTEM AND METHOD,” which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The technical field relates to engine feedback control for an internalcombustion engine, and more particularly, to an engine feedback controlsystem and method for reducing engine operation variations.

BACKGROUND

Design of internal combustion engine systems involves developing controlsystems for controlling exhaust gas recirculation (EGR) fraction, chargeair mass flow (MCF), fueling, injection timing, and so on, to meetperformance and emissions targets. Control is often carried out by anengine control module (ECM) (also called the engine control unit (ECU))or some other controller utilizing an engine map and/or tables in whichpre-calibrated reference values are associated with inputs defining arequested operating condition, such as requested engine speed and load.Reference values can include intake or engine out oxygen concentration,engine out “lambda” (λ), which is the ratio of the air/fuel to thestoichiometric air/fuel value, and engine out nitrogen oxides (known asNOx), all of which can be measured directly or indirectly (e.g., by wayof a virtual sensor). The ECM/ECU receives the measured or determinedactual values as a feedback signal to a controller, which adjustsactuators of the engine system (e.g., actuators controlling an EGRvalve, fuel injectors etc.) based on differences between thepre-calibrated reference values and corresponding determined actualvalues (e.g., NOx or sensor feedback signals) to minimize thesedifferences or otherwise cause the measured/determined values toconverge towards the pre-calibrated reference values.

SUMMARY

This disclosure provides a system and method for controlling an internalcombustion engine that can reduce or minimize variation among pluralengines. The control utilizes a single-input-single-output (SISO) schemethat adjusts an operating parameter of an internal combustion enginebased on a difference between a reference value of an emissionscharacteristic and sensed value of that emissions characteristic.

In one aspect, a SISO control system for an internal combustion engineincludes selection module configured to select, for an operating point,one operating parameter lever and one emissions characteristic, wherethe operating parameter lever is related to one of exhaust gasrecirculation (EGR) and charge air mass flow (MCF). A referenceretrieving module is adapted to retrieve a pre-calibrated referencevalue of an associated with the selected emissions characteristic, wherethe pre-calibrated reference value is based on predetermined referencedata associated with a respective operating point of the internalcombustion engine. The SISO control system includes a differencecalculating module adapted to receive a signal corresponding to ameasured value of the emissions characteristic and calculate adifference between the pre-calibrated reference value and the measuredvalue, and a controller adapted to provide a control signal based on thecalculated difference. An operating parameter adjustment module isadapted to receive the control signal, determine an adjustment factorvalue based on the control signal and the operating point, retrieve astored operating parameter reference value related to selected operatingparameter lever for the respective operating point, and adjust the valueof the stored operating parameter reference value by an amount based onthe adjustment factor value.

In another aspect of the disclosure, a method of controlling an internalcombustion engine includes the processes of receiving operatingparameters for operating the internal combustion engine at an operatingpoint, determining, for the operating point, one operating parameterreference lever and one emissions characteristic, where the operatingparameter reference lever is related to one of exhaust gas recirculation(EGR) fraction and charge air mass flow (MCF), retrieving a referencevalue of the emissions characteristic based on predetermined referencedata and the requested operating point, receiving a signal correspondingto a measured value of the emissions characteristic, and determining acontrol signal based on the difference between the retrieved referencevalue and the measured value. The method further includes determining,using a processor, an adjustment factor value based on the controlsignal and the requested operating point, retrieving a stored operatingparameter reference value associated with the determined operatingparameter reference lever for the current requested operating point, andadjusting, using the processor, the value of the operating parameterbased on the determined adjustment factor value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an internal combustion engine control systemaccording to an exemplary embodiment.

FIGS. 2A to 2F are probability distribution graphs for EGR, MCF, Fuel,exhaust O₂, and NOx including noise only at an exemplary operating mode.

FIG. 3 is a diagram showing exemplary probability distributions of EGR,Fuel, NOx, exhaust O₇, and λ including bias and noise for a sample ofengines.

FIG. 4A shows a distribution of O₂ including bias and noise for anengine with bias and a distribution of O₂ for a baseline engineincluding noise only, and 4B shows an adjustment of the mean for thedistribution of O₂ including bias and noise towards the mean of thenoise only distribution.

FIG. 5 is a diagram of a layout of a NOx-EGR fraction SISO controlsystem for determining a reference X_(EGR) fraction value for a steadystate operating condition of an internal combustion engine according toan exemplary embodiment.

FIG. 6 is a diagram of an exemplary layout of a NOx-EGR fraction SISOcontrol system for determining a reference X_(EGR) fraction value for atransient state operation based on an adjusting factor determined for asteady state operation of an internal combustion engine according to anexemplary embodiment.

FIG. 7 is a system diagram of an internal combustion engine systemincluding SISO control according to an exemplary embodiment.

FIG. 8 is a diagram of an exemplary process for selecting a controller.

DETAILED DESCRIPTION

The inventors realized that variation between engine systems can resultfrom bias (i.e., noise from one engine to another engine), random noise(i.e., noise within one engine) and sensor noise, and can causevariations in engine out emissions such as particulate matter (PM). Forexample, bias can arise from engine-to-engine differences in EGR systems(Bias_(EGR)), mass charge flow systems (Bias_(MCF)), and/or fuel systems(Bias_(fuel)), random noise within an engine in the EGR systems(e_(EGR)), mass charge flow systems (e_(MCF)), and/or fuel systems(e_(fuel)), and noise in the sensors readings, such as noise in the O₂,and NOx sensor outputs. This noise can cause variations in amounts ofemissions output from one engine operating in a particular mode to bedifferent from emissions output from another same type of engineoperating in the same mode and using the same pre-calibrated operatingparameters. This disclosure describes a system and method including acontrol strategy that can adjust, in an engine system having noise andbias, one or more pre-calibrated, or baseline reference values utilizedby a controller of the engine system that controls the engine systemoperation. The system and method updates, rewrites or builds a newengine map (e.g., lookup tables) over plural modes to minimizediveensions in the engine out emission levels and/or ensure compliancewith emissions requirements.

Many aspects of this disclosure are described in terms of sequences ofactions to be performed by elements of a driver, controller, controlmodule and/or a computer system or other hardware capable of executingprogrammed instructions. These elements can be embodied in a controllerof an engines system, such as an ECM (ECU), or in a controller separatefrom, and communicating with an ECM/ECU. In an embodiment, thecontroller and/or ECM/ECU can be part of a controller area network (CAN)in which the controller, sensor, actuators communicate via digital CANmessages. It will be recognized that in each of the embodiments, thevarious actions for implementing the control strategy could be performedby specialized circuits (e.g., discrete logic gates interconnected toperform a specialized function), by program instructions, such asprogram modules, being executed by one or more processors (e.g., acentral processing unit (CPU) or microprocessor), or by a combination ofboth, all of which can be implemented in a hardware and/or software ofthe ECM/ECU and/or other controller or plural controllers. Logic ofembodiments consistent with the disclosure can be implemented with anytype of appropriate hardware and/or software, with portions residing inthe form of computer readable storage medium with a control algorithmrecorded thereon such as the executable logic and instructions disclosedherein, and can be programmed, for example, to include one or moresingular or multi-dimensional lookup tables and/or calibrationparameters. The computer readable medium can comprise a random accessmemory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), an optical fiber, and aportable compact disc read-only memory (CD-ROM), or any othersolid-state, magnetic, and/or optical disk medium capable of storinginformation. Thus, various aspects can be embodied in many differentforms, and all such forms are contemplated to be consistent with thisdisclosure.

FIG. 1 is a diagram of an exemplary SISO (single-input-single-output)internal combustion engine control system 1 that can adjust for noise inengine subsystems, such as EGR, MCF, and fuel subsystems, among pluralinternal combustion engine systems to minimize corresponding variationsin engine out emissions over plural operating modes. As shown in FIG. 1,an internal combustion engine system 10 operates based a. requestedengine speed and fueling rate, for example, as requested by an operatorof a vehicle powered by the engine or as set for a stationary engineapplication. The engine system 10 includes cylinders formed in an engineblock (not shown). Each of the cylinders contains a reciprocating pistonand is covered with a cylinder head including intake and exhaust valvesto define a combustion chamber. An intake valve (or valves) associatedwith each cylinder is fluidly connected to an intake manifold (notshown) by way of intake port and the exhaust valve (or valves)associated each cylinder is fluidly connected with an exhaust manifold(not shown) by way of an exhaust port. The exhaust manifold has anoutlet for supplying EGR gas to a mixer in which intake air and the EGRgas mix before being provided to the intake manifold. The amount of EGRfraction in the air/exhaust gas mixture can be metered by way of an EGRvalve mechanism controlled by an actuator. The MCF of intake airsupplied to each cylinder also can be metered by one or more mechanismsthat are actuator-controlled. For example, an engine system can includea vari ble geometry turbocharger (VGT), a throttle, and a turbochargerbypass valve (not shown).

The requested operation is depicted in FIG. 1 as engine speed commandSpeed_(cmd) and fuel rate command Fuel_(cmd). These commands areprovided to a set of static lookup tables 20 to determine apre-calibrated reference value for each of command parameters MCF(MCF_(cmd)) and EGR fraction (X_(EGRcmd)), and engine out O₂, engine outengine out NOx, and intake O₂ corresponding to a current operating pointor mode defined by the command parameters. In response, one or more ofthe lookup tables 20 provide a. reference signal corresponding to thereference value to signal path 22. The term “pre-calibrated” is usedherein to describe a predetermined value derived by experiment and/orcalculation and represents a baseline value corresponding to a requestedengine speed and fueling requirement. A pre-calibrated value issometimes referred to herein as a “normal” or “nominal” (noise-free)value that is predetermined, stored in memory, and accessible by theengine system ECM/ECU (or other engine system controller).

As shown in FIG. 1, the engine system 10 can be subject to one or morenoise sources, such as the depicted Bias_(EGR), Bias_(MCF), andBias_(fuel) (bias noise from engine-to-engine), e_(EGR), e_(MCF), and/ore_(fuel) (random noise within an engine) and/or other noise sources. Forexample, fuel system errors can include, but are not limited tomechanical variation among injector profiles via manufacturingprocesses, pressure variation related to sensor profiles, creep/wear ofthe fuel system, and electrical related errors. Studying the baselineengine system under random noise provides a mean and standard deviation,or sigma (σ) value for each of the outputs O2 (intake and exhaust), λ,and NOx of the engine system 10. These mean values can be used asreference, or pre--calibrated outputs.

FIGS. 2A to 2F show exemplary baseline probability distribution graphsfor EGR, MCF, Fuel, exhaust O₂, λ, and NOx for a B75 mode of a HDCCdriving cycle where the 3σ values of noise is 2% for EGR, MCF, Fuel,2.5% for O₂ sensor noise, and 5% for NOx sensor noise. As can be seen,the median and mean for each curve is close, and hence it can be assumedthat distributions are normal. For each of O₂ and the statistical mean(random noise due to sensing) is close to the nominal (noise free)value. Using these findings, a statistical analysis of bias in an enginesystem can be performed to capture engine-to-engine variation.

FIG. 3 is a diagram showing exemplary bias distributions of an enginesample and two engine systems, Engine 1 and Engine 2, lie in each biasdistribution. As can be seen from FIG. 3, Engine 1 and Engine 2 responddifferently, relative to one another, to a same commanded triplet: MCF,EGR and fueling. The mean of the bias distributions shown in FIG. 3 thebaseline, or nominal engine value. For Engine 1 shown in FIG. 3, the EGRfraction is positively biased, the MCF is negatively biased, and thefueling is negatively biased compared with the nominal mean values. ForEngine 2, the EGR fraction is negatively biased, the MCF is positivelybiased, and the fuel is negatively biased compared with the nominal meanvalues.

To determine statistics with bias and noise, an analysis can be run asfollows. Each engine is considered to be an input-output system with thefollowing inputs: FOR, MCF and Fuel and the following outputs: NOx, O2and λ. The population of engines is modeled as a statisticaldistribution with the properties of the nominal engine as mean values(i.e., the EGR, MCF and Fuel of the nominal engine will be the meaninput values, and, the corresponding NOx, O2 and λ will be the meanoutput values). The standard deviation of this distribution can bechosen as, for example, as corresponding to EGR Fraction: 2%, MCF: 4%,and Fuel: 2%. From this distribution, the above Engine 1 will have EGR,MCF and Fuel different from the mean, but within the bias distribution.Similarly Engine 1 will have NOx, O2 and different from the mean, butwithin the distribution for the outputs. The inputs and the outputs aredifferent from the mean because Engine I is not the nominal engine. ForEngine 1, we can command the mean EGR, MCF and Fuel as shown in FIG. 3,but due to measurement noises, actuator noises, and/or other noises,these values will not be carried out. So, for that one engine, Engine 1,the noise is added to the inputs and measurement noise and get theoutput, for example, adding the following noise EGR Fraction: 2%, MCF:2%, O₂ sensor noise: 2.5%, and NOx sensor noise: 5%, 10%, or 15%. Thisis repeated using a different noise to the inputs and measurement andget the output over many times (e.g., thousands of times) for justEngine 1, to give a distribution for that one engine. We can makesimilar determinations for Engine 2, and other engines taken from theengine population. Hence, the effects of bias (engine to enginevariation) and noise (variation within a single engine) can bedetermined by choosing different bias value sets for the triplet [EGR,Fuel], and for each bias triplet above representing one engine (i.e.,EGR, MCF, and Fuel), values of Nx, O₂, and λ corresponding to variousnoise values can be evaluated and determined. The mean value of NOx, O₂,and λ for this engine can be determined from these corresponding values.The mean and the a of the NOx, O₂, and λ provide the mean and the a ofnoisy data with bias.

A strategy of the internal combustion engine control system 1 is to movethe biased plus noise mean value of the NOx, O₂, and/or λ statisticdistribution to be controlled towards the noisy mean value utilizing oneof two levers: EGR fraction (X_(EGR)) and MCF, and the value one of fourphysical or virtual sensors measuring an emissions characteristic,namely exhaust O₂, NOx, λ and intake O₂. Returning to FIG. 1, the SISOinternal combustion engine control system includes controller selectionlogic 24, which can be associated with and/or included with the lookuptables 20. For each requested or expected operating point, controllerselection logic 24 determines whether to control MCF or EGR fraction asa lever to manipulate one of the emissions characteristics exhaust O₂,λ, NOx, and intake O2 to compensate for bias in the engine system 10. Inother words, based on a current or expected operating mode speed/torquedemand, controller selection logic 25 determines which one of eightcontrollers operates to adjust an amount of O₂ and/or NOx output fromthe engine system 10. Selector 23 selects one of exhaust O₂, X, and NOxintake O₂ based on the selected controller selection logic 24 andprovides the selected measured value on feedback path 25 e.g., as a CANmessage). After selecting a controller i.e., an operating parameterlever and sensor pair), the internal combustion engine control system 1adjusts the operating parameter lever according to a closed-loopfeedback signal to move the emissions characteristic mean towards themean of the baseline engine.

FIGS. 4A shows an example of a noise distribution curve 40 related to anuncontrolled emissions characteristic, here O₂ fraction, where thedistribution includes bias and random noise and is centered about biasmean 42. Also shown in FIG. 4A is the noise distribution curve 44 for anoperating point corresponding to the pre-calibrated statistics for O2.Distribution curve 44 includes only random noise for the operatingpoint, where the O2 fraction values are distributed about mean 46. Theaim of the controller selected by controller selection logic 24 is tomove the biased mean 42 towards the mean 46, as shown in FIG. 4B. Forexample, if exhaust O₂ is controlled by EGR fraction as the lever, thebias mean 42 must tend towards the mean 46 of the noise onlydistribution 44.

FIGS. 4A and 4B also show a confidence interval centered on the mean 46and equal to 2(x)(σ), where x is chosen to define a degree of confidence(i.e., increasing the value of x increases confidence, with x=1corresponding to about 85% confidence). In an embodiment, the amount ofmovement of the mean 42 can depend on a set confidence level. Forexample, if the bias mean 42 lies within the confidence interval, thenit is considered that it cannot be distinguished from noise and is notmoved (i.e., no control action taken). If the bias mean 42 lies outsidethe confidence interval, as shown in FIG. 4B, the bias mean can be movedto at least the nearest confidence boundary via control of EGR or MCF,as shown by the arrow labeled “Minimum.”

The amount of movement of the bias and noise mean 42 is calculated usinga feedback loop. Referring again to FIG. 1, a controller 26, forexample, a PID (i.e., proportional-integral-deriva(ive) controller,operates to minimize error signal “e” corresponding to the differencebetween the feedback signal on path 24 and the reference signalcorresponding to the pre-calibrated reference value on signal path 22.The controller 26 generates a control signal based on the value of theerror signal e, and provides the control signal to signal path 30leading to adjustable lookup tables 32. The adjustable lookup tables 32receive the control signal output by controller 26 and generate MCFcommand MCF_(cmd) and EGR fraction command X_(EGRcmd) based on thecurrently requested Speed_(cmd) and Fuel_(cmd) commands and the controlsignal. The X_(EGRcmd), MCF_(cmd) and Fuel_(cmd) commands are thenprovided to the respective EGR, MCF, and fueling subsystems of theinternal combustion engine system 10.

In an embodiment, the adjustable lookup tables 32 include tables relatedto steady state operating conditions, known as α₁ lookup tables, forsteady state reference value lookups, and tables related to transientstate operating conditions, known as α₀ lookup tables, for transientstate reference value lookups related to transient operating conditions.Initially, the α₁ and α₀ lookup tables can be populated with datarelated to pre-calibrated (nominal) values, such as target referencevalues of a baseline engine necessary for compliance with governmentmandates. However, during operation of the engine system 10, the α₁lookup tables are adjustable as a function of the error signal eprovided to the controller 26 to account for variations resulting fromnoise in the engine system 10 and/or sensors (not shown).

The sensors of engine control system 1 includes an O₂ model 34 and anNOx model 36, which respectively calculate the engine out O₂ fractionand the engine out NOx amounts. The MCF, EGR fraction and Fuel inputs tothe O₂ Model 34 and NOx Model 36 can be measured values or estimates.For example, EGR could be measured and MCF and Fuel could be estimates.Engine system 10 can have either real sensors to measure these values orcode in the ECM to estimate these values. The exhaust O₂, NOx, andintake O₂ can readily be derived from the model outputs and provided toselector 23, which selects one of the derived values according to themonitored parameter of the selected controller and provides a signalcorresponding to the selected value on the feedback path 25. Thesemeasured values include bias and random noise from the subsystemscontrolling the EGR, MCF and fuel provided to the Engine System 10(where the bias and random noise are depicted as separate inputs in FIG.1). The following examples for the models can comprise code forcalculation various elements of the virtual elements of the model can bereplaced with physical sensors, for example, the φ or O₂(%) calculationbelow can be replaced by a physical sensor.

The O₂ model 34 can utilize an equation based model based on thechemical reaction equation:

ɛϕ CH_(y) + (O₂ + ψ N₂) → ɛ ϕ CO₂ + 2(1 − ɛ)ϕ H₂O + (1 − ϕ)O₂ + ψ N₂where:${ɛ = \frac{4}{4 + {y\left( {1.8\mspace{14mu} {for}\mspace{14mu} {\# 2}\mspace{14mu} {diesel}} \right)}}},{\psi = 3.773},{\phi = {\frac{1}{\lambda} = {\frac{\left( \frac{A}{F} \right)_{s}}{\left( \frac{A}{F} \right)\;} = {\frac{14.5\left( {{for}\mspace{14mu} {\# 2}\mspace{14mu} {diesel}} \right)}{\frac{A}{F}} = {\frac{14.5{\overset{.}{m}}_{f}}{{\overset{.}{m}}_{a}} = \frac{14.5{\overset{.}{m}}_{f}}{{\overset{.}{m}}_{CF}\left( {1 - X_{EGR}} \right)}}}}}},{{{and}\mspace{14mu} {O_{2}(\%)}} = {100*\frac{1 - \phi}{{\left( {1 - ɛ} \right)\phi} + 1 + \phi}\mspace{14mu} {where}\mspace{14mu} \phi \mspace{14mu} {is}\mspace{14mu} {the}\mspace{14mu} {equivalence}\mspace{14mu} {{ratio}.}}}$

Alternatively, O₂ model 34 can determine the O₂ fraction in the exhaustbased on the oxidation of diesel fuel under lean operating conditionsusing an iterative process.

The NOx Model 36 can be, for example, a regression model based on MCF,EGR, rail pressure, final timing, main quantity, and post quantity; amodel based on direct lookup table using test cell data; and an MLR(Multiple Linear Regression) model. In an MLR model, MCF, EGR fraction,and total fuel qty. are the independent variables (IVs) and are inputsto a 3D NOx lookup table. Each of the IV's are measured values or anoutput of a virtual sensor based on some measured value. The MLR datacan be smoothed and unknown areas of table can be extrapolated to knownareas.

The internal combustion engine control system I is particularly usefulfor controlling amounts of PM and NOx emissions output from an enginesystem. For example, an embodiment focusing on managing PM output amonga population of engines will attempt to mitigate an atnount of PMcoining out of off-nominal engines in that population to reduce dieselparticulate filter (DPF) failures. Because PM is very much dependent onvalue, if the balance and other critical parameters are controlled witthrespect to the baseline engine through the levers of X_(EGR) and MCF,then excursions or deviations of PM in off-nominal engines can beavoided and design targets can be moved within or closer to a targetemissions limit.

The relationship between NOx and PM is understood, and it is alsounderstood that NOx is heavily controlled by the amount of EGR exhaustgas flowing into the intake manifold of the engine system 10. Reducingan amount of NOx can involve adding more EGR to the intake of the enginesystem 10, and reducing an amount of PM can involve increasing an amountof λ increase the amount of air to make fuel burn more completely. Asmore air is added, more NOx is produced; and with less air added, morePM is produced. Hence, there is a tradeoff between PM and NOx outputs.However, in different parts of an engine's operating map, NOx can bemore dependent on MCF compared with EGR fraction, and also can be afunction of how the engine is calibrated. Thus, a selection of whichlever to be used (i.e., EGR fraction or MCF) for adjusting a particularemission product can depend, or be based on whether the engine isoperating in a steady state mode or a transient state mode. Where aparticular engine is operating in those modes, and can be different fordifferent engine types at a same operating point.

Using internal combustion engine control system 1, an engine in thefield can determine whether it is going off calibrated targets based onsignals of its physical or virtual sensors. For example, using a signalfrom a NOx sensor in the exhaust stream downstream of a turbocharger(not shown), the controller 26 would be able to determine whether thevalue indicated by the NOx sensor signal, which indicates the actualengine out NOx level, corresponds to what the NOx emission should bebased on a pre-calibrated reference value. If the controller 26determines that a difference exists between the sensed andpre-calibrated values, it can take that difference into account andstart adjusting an operating parameter reference value .e., the MCF orEGR fraction) as a lever to help bring the engine out NOx target towhere it should be, and if combined correctly with λ control, PM canalso be controlled within a target value.

FIG. 5 shows a more specific example of a layout of an engine outNOx-EGR fraction SISO control system 2 that controls NOx via anadjustment of a reference EGR fraction value X_(EGR) stored in anadjustable lookup table 32 for a current steady state operatingcondition. The layout of control system 2 can be part of an enginecontroller (e.g., the ECM/ECU logic). More specifically, for a requestedengine speed (ES) value, engine load (EL) value, fueling rate inputvalue, noisy EGR input value and/or MCF input value, an expected NOxreference value can be calculated at NOx reference calculation module48, for example, using a pre-calibrated lookup table. In an embodiment,MCF and EGR input values can be determined using a current value of theX_(EGRcmd) or MCF_(cmd) in the α₁ or α₀ reference tables, where choiceof an α₁ or α₀ table depends On the whether the requested operation is asteady state mode or a transient mode. An error signal “e” is providedon signal path 28 and corresponds to a difference between the calculatedNOx reference on signal path 22 and a feedback signal on signal path 25related to an engine out NOx sensor reading. The controller 26 receivesthe error signal and outputs a control signal value corresponding to thevalue of the error signal to signal path 30.

An α₁ tuning factor table 50 can be a pre-calibrated table receives asinputs the control signal on signal path 30 and the requested ES and ELvalues and determines a tuning factor based on the received inputs andprovides the tuning factor on signal path 51. Meanwhile, an X_(EGR) α₁reference table 52 determines an X_(EGR) fraction value for steady stateoperation based on the requested ES and EL and provides a signalcorresponding to the determined X_(EGR) fraction value on signal path53. The initial or default values contained in the X_(EGR) α₁ referencetable 51 can be pre-calibrated (nominal) values associated with abaseline engine. The signals on signal paths 51 and 53 combine using amultiplication process to provide an adjusted X_(EGR) fraction α₁reference value 54. The adjusted X_(EGR) fraction α₁ reference value 54can be used to build an updated X_(EGR) fraction α₁ reference table orto adjust the X_(EGR) fraction value in a pre-calibrated α₁ referencetable 52 based on the tuning factor output from the X_(EGR) α₁ tuningfactor table 50. Also shown in FIG. 5 is an X_(EGR) α₁ limiter table 56,which can be provided to monitor the generated tuning factor and controlsignal for a current operating condition and prevent generating a tuningfactor greater than a practical limit for that operating condition.

While the SISO control system 2 shown in FIG. 5 is an engine out NOxcontroller using EGR fraction as the target lever, this is only one ofplural possible SISO candidate controllers that can be utilized for aspecific operating point, eight of which are shown in Table 1:

TABLE 1 Controlled Parameter Operating Parameter (lever) 1. Engine outO₂ EGR fraction 2. Engine out O₂ MCF 3. Engine out λ EGR fraction 4.Engine out λ MCF 5. Engine out NOx EGR fraction 6. Engine out NOx MCF 7.Intake-O₂ EGR fraction 8. Intake-O₂ MCF

Other controllers are possible, such as those based on fueling as theoperating parameter. One feature of the overall strategy is that insteadof focusing on one sensor/actuator pair, different combinations can betested considering the relationships among EGR fraction, MCF, NOx, PM,etc. For example, for different operating regions, different controllerscan be used depending on the control performance. Preferably, at anyparticular operating mode, the lever (i.e., EGR position, MCF positionetc.) that has the maximum effect on the outputs (NOx, PM, Intake O2 orexhaust O2) is determined. In other words the sensitivity of each of theinputs to each of the inputs in determined and the input-output pairwith the maximum sensitivity can be chosen as the controller at thatpoint.

The present disclosure provides a simplified SISO controller thatcontrols one of NOx, intake O₂ and exhaust O₂, for an operatingcondition, by adjusting only one engine operating parameter selectedfrom X_(EGR) fraction, adjust MCF, or fueling rate as opposed to a morecomplex system that elaborates on the controller (e.g., a multiple inputmultiple output (MIMO) system). In any given region on the engine map,the most impacting target reference is known, i.e., EGR fraction, MCF,or fueling, and therefore in a particular operating region one of EGRfraction, MCF, or fueling should change, or be adjusted to control NOx,PM and O₂. As long as controlled target is converging to the nominalvalue, then the adjustment going the right way and will start adjustingthe references for EGR, MCF or fueling in an online fashion foroff-nominal engines that are not meeting the specification. Therefore,the SISO system makes efficient use of sensor reading and finds the mosteffective operating parameter lever (EGR fraction, MCF, or fueling) formore uniform performance among the off-nominal engines.

For a transient mode α₀ reference, the control signal is unable toconverge to an appropriate gain factor due to the transient nature ofthe engine operation. To solve this problem, the whole engine operatingarea can be divided into many cells according to x index /(engine speed)and y index (total fueling/load) of the α₁ tuning table. Since theengine will visit some cells more frequently than others, all cells canbe ranked according to the density of FTP points in each cell and somecells with low visiting frequency can be overlooked. For example, thetop 20 cells can constitute a specific driving cycle for generating α₁tuning factors first, although finer granularity of control can begained if this tuning function is explored for the entire driving map. Acalibrated fraction of the steady state α₁ gain factors can then be usedto determine the transient state α₀ reference values of transient modeoperation.

FIG. 6 is a diagram of an exemplary layout of an engine out NOx SISOcontrol system 3 that controls NOx via an adjustment of a referenceX_(EGR) fraction value for steady state operations as described above,and adjusts a reference X_(EGR) fraction value for transient stateoperations based on the adjusting factor determined for the steady stateoperation. Elements having the same reference numbers as those in FIGS.1 and 5 are described above. The controller system 3 carries out anotherfeature of the disclosure, which extends the steady state benefit totransient state. More specifically, the strategy of the SISO controller3 includes using a tuning factor generated by the α₁ tuning factor tablein the determination of an adjusted transient state operating parameterreference value for transient state mode of operation.

With reference to FIG. 6, the tuning (adjusting) factor output on path51 from the α₁ tuning factor table 50 is a number greater or less than1, but in the neighborhood of 1 (e.g., 1.01 or 0.99). The tuning factoris multiplied with the X_(EGR) (i.e., the EGR fraction) value output bythe X_(EGR) α₁ (steady state) reference table 52 for that operatingcondition (i.e., engine speed (ES) and engine load (EL)). Thismultiplication scales the current X_(EGR) reference value up or downbased on the error signal provided to the PID controller 26, whichgenerates the new X_(EGR) reference value 54 for the X_(EGR) α₁reference table 52. To generate an adjusted X_(EGR) α₀ reference value64 for the X_(EGR) α₀ (transient) reference table 62, the percentagechange provided by the α₁ tuning table can be calculated by subtracting“1” (e.g., for a tuning factor of 1.01, a 1% adjustment) and use thetuning factor output from X_(EGR) α₀ tuning factor table 60 to generatea fraction of the fraction, or a percent of the percent change. Forexample, for a 1% adjustment for α₁, and a 30% impact represented by avalue 0.3 on path 65 from the X_(EGR) α₀ tuning factor table 60, themultiplication would result in 0.003, to which “1” is added back togenerate an effective 1.003 output on path 67 from the α₀ tuning factortable 60. The effective X_(EGR) α₀ tuning factor on path 67 ismultiplied with the X_(EGR) α₀ reference value on path 69 to provide theadjusted X_(EGR) α₀ reference value 64, which is used as an X_(EGR) α₀reference value in a new X_(EGR) α₀ reference table or to replace theX_(EGR) α₀ reference value at the transient operating condition in theexisting reference table. Other embodiments can use different respectiveschemes to determine a X_(EGR) α₀ tuning factor based on the calibrationdetermined for the X_(EGR) α₁ tuning factor.

FIG. 7 is a diagram showing an exemplary internal combustion enginesystem 4 that can adjust operating parameters (MCF, EGR fraction, orfueling) to compensate for variations in engine out emissions (i.e., PMand/or NOx) resulting from engine-to-engine variation. The internalcombustion engine system 4 includes an ECM 100 and powertrain system150. In an embodiment, plural modules and memory containing datastructures that are configured to perform various system functions areintegrated into the ECM 100, although in other embodiments, one or moreof the depicted modules can be implemented in a module separate from theECM. The ECM 100 also can include fewer or more modules in addition tothose shown.

The ECM 100 includes an actuator control module (ACM) 102 that receivesa requested or expected engine speed and engine load, a referenceretrieval (RR) module 104 that retrieves operating parameters fromlookup tables 106 based on the requested or expected engine speed andengine load, and an actuator positioning control (APC) module 108 thatcontrols the actuators 110 of the powertrain system 150 based on theretrieved reference values. ECM 100 further includes an operationparameter adjustment (OPA) module 112, a processor (e.g., amicroprocessor, CPU) 114, a soot load/particle filter (PF) managermodule 116, an NOx sensor module 118, an O2 sensor module 120, anoperator interface 122, and a communication module 124. The powertrainsystem 150 further includes n engine 152 and sensors 154. The componentsof internal combustion engine system 4 communicate via a network 160,which can be, for example, a controller area network (CAN). Although notshown, the engine system 4 can include a number of additionalcomponents, such as an aftertreatment system including, for example, aPF (e.g., a DPF), a diesel oxidation catalyst (DOC) and/or a selectivecatalytic rejection (SCR) catalyst.

As shown in FIG. 7, lookup tables 106 include pre-calibrated (PRE-CAL.)tables 126 that contain data structures including baseline or defaultsteady state operating parameter reference values for each requestedengine speed and load (torque). The reference values can include thecorresponding fueling, injection timing, MCF, and EGR fraction. Lookuptables 106 also include actuator positioning information related to thereference values, for example, throttle position, VGT bypass valveposition, EGR valve position, etc., which the APC module utilizes toposition actuators 110 of the powertrain system 150. Pre-calibratedtable 126 additionally includes reference values for engine out O₂, λ,and NOx, and intake O₂ associated with each requested pair of enginespeed and power.

Lookup tables 106 include adjustable tables 128 corresponding to a leasta subset of the pre-calibrated table listings. For example, adjustabletables 128 can include a complete set of operating parameter referencevalues and the pre-calibrated tables 126 can be stored as read-onlydefault or reset values. The adjustable tables 128 can be initializedusing the pre-calibrated operation parameter reference values, andthereafter the stored MCF and EGR fraction targets associated with arequested pair of engine speed and load periodically, intermittently, orcontinuously updated (tuned or adjusted) based on current MCF or EGRfraction values for the requested or expect engine speed and load, and atuning factor stored in tuning factors table 130. A tuning factor is anumber around the value of one, and can be retrieved using a signalgenerated by controller 26 based on the difference between one of theengine out O0 ₂, λ, and NOx, and intake O₂ reference values stored inthe pre-calibrated tables 126 and/or adjustable tables 128 and a sensedvalue of the engine out O₂, λ, and NOx, and intake O₂.

Adjustments to the adjustable tables are carried out by the OPA module112. The OPA module 112 includes a controller selection module 132 thatincludes the controller selection logic 24 that, when executed byprocessor 114, selects a controller having a suitable parameter lever,MCF or EGR fraction, and an associated sensor feedback from among pluralsensors 144 monitored by a sensing monitoring module 134 (see, reference23 of FIG. 1), for a currently demanded or expected engine speed andload.

In an embodiment, the controller selection module accesses apredetermined table (not shown) having a listing of controllers (seeTable 1) associated with engine speed and load operating points forwhere each association is based on simulated or calculated conditions atvarious operating modes and interpolated points therebetween. In anexemplary embodiment, choice of either EGR fraction or MCF as the levercan depend on which one contributes more to exhaust O₂ fraction, λ, NOx,or intake O₂ variation.

FIG. 8 shows an exemplary process flow 80 for selecting a controllerfrom among eight available controllers, although it is to be understoodthat a similar method can be applied where more or less than eightcontrollers are available. In the exemplary process flow 80, process 82associates weighting factors to each of NOx and smk (particulate matteror smoke) based on preference, engine operating point or other criteria.For example, for equal weight, NOx can be associated with weightingfactor A=0.5, and smk can be associated with weighting factor B=0.5.Weighting factors also are associated with each operating mode. Forexample, each of the twelve FTP modes A25, A50, A75, A100, B25, B50,B75, B100, C25, C50, C75, C100 can be assigned a weighting factorW_(mi), where i=1, 2, . . . 12. Next, process 84 determines the percentimprovement in NOx variation reduction as NOx_%_j,i, and process 86determines the percent improvement in smk variation reduction assmk_%_j,i, each of which is based on a change in the standard deviationfrom an uncontrolled stated to a controlled state. Here, the “j,i”represents that for each one of the controllers j, where, for example,j=1, 2, . . . 8, the percent improvement in NOx and smk variationreduction is determined for each mode i, where, for example, i=1, 2, . .. 12. In an embodiment, this can be carried out utilizingsimulations/studies to determine performance for various combinations ofspeed/torque and in various modes, which can be encoded into a lookuptable in the controller selection logic 24. Next, process 88 determinesthe cost of each controller at each mode: Con_(j) _(—)m_(i)=(A*NOx_%_j,i+B*smk_%_j,i)*W_(mi), where j=1, 2, . . . 8 and i=1,2, . . . 12. Next, process 90 determines each controller's cost: C_(j)at all modes, where j=1, 2, . . . 8. For example, C_(i)=sum{Com_mi},where i=1,2, . . . 12. In process 92, the controller having the maximumcost at all modes is selected as the controller: controllerselection=max{C₁, C₂, . . . C₁₂}.

Returning to FIG. 7, adjusted parameter calculation module 136 of OPAmodule 112 includes logic executed by processor 114, which tracks anerror between the reference value and sensed value of exhaust O₂fraction, NOx, or intake O₂, and modifies the MCF or EGR fraction targetvalue using a tuning factor from tuning factor table 130 based on thetracked error at an operating point and stored (e.g., updates) thetarget value for that operating point in the adjustable table 128. Thesensed reference value can be provided by NOx sensor module 118 or O₂sensor module 120, each of which can calculate the engine out NOx and O₂fraction based on virtual and/or physical sensors, although and intakeO₂ can be derived from outputs of engine out NOx and O2 sensor modulesor sensed in a more direct manner. For example, an intake manifold O₂sensor can be used to measure intake O₂, an exhaust O₂ sensor can beused to measure exhaust O₂, and an NOx sensor can be used to measureNOx. Each such sensor output is a direct measurement available in theengine. In another example, O₂ (intake or exhaust) can measuredindirectly based on CO₂ measurements and fuel quantity. For eachrequested or expected ES and EL pair, the ECM 100 includes logic of anactuator adjustment module (not shown) that causes actuators 146 of thepowertrain system 140 to move to a position to achieve current targetMCF or EGR fraction parameter values stored in the adjustable lookuptables 128.

The adjusted parameter calculation module 106 can include logic thatdetermines a transient state operating parameter reference valueassociated with a transient state operating mode, for example, asdescribed above with respect to FIG. 6. For example, the pre-calibratedtables 126 and tuning factor tables 130 also can include tables relatedto transient state operation. For example, transient state tuning factortables can based on a fractional amount of the steady state tuningfactor generated by the controller 26 and steady state tuning factortable, and the reference operating parameter reference values for eachrequested transient state engine speed and load (torque) values can beadjusted based on the steady state tuning factors and transient statetuning factors stored in tuning tables 130. Similar to the steady statetables, the transient state tables can the initialized at pre-calibratedtransient state reference values, and thereafter adjusted.

The soot load/PF manager module 116 includes logic for estimating sootload (i.e., PM loading) in the PF and can execute regeneration routineperiodically or intermittently, based on the estimated condition, tooxidize soot in the filter. Operating an internal combustion enginesystem with adjusted MCF and EGR fraction targets results in less PMvariation from engine-to-engine, and thus more accurate PM estimates.

The operator interface 122 of the ECM 100 receives input from the systemoperator, such as requests for operation at a specific engine speed (ES)and load (EL), for example, based on the position of an acceleratorpedal. Operator interface 122 also can provide the operator with statusof various system components and allow the operator to manipulateenvironmental conditions and display output. Communication module 124(e.g., a CAN network module) can include a GPS unit 138 to receiveinformation to determine coordinate positioning and/or supply data inadvance of an operation or forthcoming positions or in real-time as thevehicle is operated and route traversed. In an embodiment, an expectedES and EL can be determined based on vehicle position and terraininformation and applied automatically in a cruise control mode.

Embodiments consistent with the present disclosure can automaticallyadjust engine operation parameters to account for engine-to-enginevariations and to optimize an amount of NOx/PM and fuel economy, whilekeeping emission below an acceptable level. This is made possible by wayof closed-loop engine control that can minimize PM variation due toengine-to-engine variation.

Additionally, embodiments of the disclosure allow for design marginsthat are closer to the emissions requirement because off nominal enginescan be brought to within specifications though adjustment of engineoperating parameter reference value for different operating conditions.

Embodiments of the present disclosure can improve PM variation amongengines and improve accuracy of soot load estimation. Since the sootload/PF manager 116 makes decisions on regeneration control tactic basedon soot load estimation, embodiments applying strategies disclosedherein can avoid excessive PF regeneration and protect theafter-treatment system.

Although a limited number of exemplary embodiments is described herein,one of ordinary skill in the art will readily recognize that there couldbe variations to any of these embodiments and those variations would bewithin the scope of the disclosure.

What is claimed is:
 1. A system, comprising: a selection circuitconfigured to select, for an operating point of an internal combustionengine, one operating parameter lever and one emissions characteristic,said selected operating parameter lever related to one of an exhaust gasrecirculation fraction or a charge air mass flow; a reference retrievingcircuit adapted to retrieve a stored pre-calibrated reference valueassociated with the selected emissions characteristic for the selectedoperating parameter lever, said pre-calibrated reference value based onpredetermined reference data associated with a respective operatingpoint of a nominal internal combustion engine; a difference calculatingcircuit adapted to: receive data corresponding to a measured value ofthe selected emissions characteristic, and calculate a differencebetween the pre-calibrated reference value of the selected emissionscharacteristic for the nominal internal combustion engine and themeasured value of the selected emissions characteristic for the internalcombustion engine; a controller adapted to provide a control instructionbased on the calculated difference; and an operating parameteradjustment circuit adapted to: receive the control instruction,determine an adjustment factor value based on the control instructionand the operating point, retrieve a stored operating parameter referencevalue related to selected operating parameter lever for the respectiveoperating point, and store an adjusted value of the stored operatingparameter reference value based on the adjustment factor value.
 2. Thesystem of claim 1, wherein storing the adjusted value of the storedoperating parameter reference value comprises storing an adjustedoperating parameter reference value in a separate adjustable steadystate reference table.
 3. The system of claim 1, wherein the emissionscharacteristic reference value is one of engine out O₂, engine out λ,engine out NO, and intake O₂.
 4. The system of claim 1, wherein saidadjustment factor value and said stored operating parameter referencevalue are associated with a steady state operating mode, said adjustmentfactor circuit is further adapted to: determine a transient stateoperating mode adjusting factor based on the operating point, retrieve astored transient state operating parameter reference value associatedwith a transient state operating mode, and store an adjusted value ofthe stored transient state operating parameter reference value based onthe transient state operating mode adjustment factor.
 5. The system ofclaim 4, wherein storing the adjusted value of the stored transientstate operating parameter reference value comprises storing an adjustedtransient state operating parameter reference value in a separateadjustable transient state reference table.
 6. The system of claim 1,wherein the controller is configured to operate the internal combustionengine based on the stored adjusted value of the stored operatingparameter reference value.
 7. The system of claim 1, further comprising:a limiter circuit adapted to: compare the determined adjustment factorvalue with a predetermined limiting value for the requested operatingpoint, and limit the determined adjustment factor value to a value notexceeding the predetermined limiting value.
 8. A method, comprising:accessing, by a controller for an engine system, one or more operatingparameters for operating an internal combustion engine of the enginesystem at an operating point; determining, for the operating point, bythe controller, one operating parameter reference lever from theaccessed one or more operating parameters and one emissionscharacteristic, said determined operating parameter reference leverrelated to one of an exhaust gas recirculation fraction or a charge airmass flow; retrieving, by the controller, a pre-calibrated referencevalue for the determined emissions characteristic, the pre-calibratedreference value based on predetermined reference data of a nominalinternal combustion engine at the requested operating point; receiving,by the controller, data corresponding to a measured value of thedetermined emissions characteristic; determining, by the controller, acontrol instruction based on the difference between the retrievedpre-calibrated reference value of the determined emissionscharacteristic for the nominal internal combustion engine and themeasured value of the determined emissions characteristic of theinternal combustion engine; determining, by the controller, anadjustment factor value based on the control instruction and therequested operating point; retrieving, by the controller, a storedoperating parameter reference value associated with the determinedoperating parameter reference lever for the current requested operatingpoint; adjusting, by the controller, the value of the stored operatingparameter reference value based on the determined adjustment factorvalue to generate an adjusted operating parameter reference value; andstoring, by the controller, the adjusted operating parameter referencevalue.
 9. The method of claim 8, further comprising controlling, by thecontroller, operation of the internal combustion engine based on thestored adjusted operating parameter reference value.
 10. The method ofclaim 8, wherein the adjusted operating parameter reference value isstored in a separate steady state reference table from the storedoperating parameter reference value.
 11. The method of claim 8, whereinthe emissions characteristic reference value is one of engine out O₂,engine out λ, engine out NOx, and intake O₂.
 12. The method of claim 8,wherein said adjustment factor value and said operating parameterreference value are associated with a steady state operating mode. 13.The method of claim 12, further comprising: determining, by thecontroller, a transient state operating mode adjusting factor based onthe operating point; retrieving, by the controller, a stored transientstate operating parameter reference value associated with a transientstate operating mode and the determined operating parameter referencelever; and storing, by the controller, an adjusted value of thetransient state operating parameter reference value based on thetransient state operating mode adjustment factor.
 14. The methodaccording to claim 13, wherein the adjusted value of the transient stateoperating parameter reference value in a transient state referencetable.
 15. A system, comprising: an internal combustion engine; and acontroller operatively and communicably coupled to the internalcombustion engine, the controller configured to: retrieve a storedpre-calibrated reference value associated with a selected emissionscharacteristic for a selected operating parameter lever, saidpre-calibrated reference value based on predetermined reference dataassociated with a respective operating point of a nominal internalcombustion engine; calculate a difference between the pre-calibratedreference value of the selected emissions characteristic for the nominalinternal combustion engine and a measured value of the selectedemissions characteristic for the internal combustion engine; determinean adjustment factor value based on an operating point of the internalcombustion engine; retrieve a stored operating parameter reference valuerelated to the selected operating parameter lever for the respectiveoperating point; and store an adjusted value of the stored operatingparameter reference value based on the adjustment factor value.
 16. Thesystem of claim 15, wherein the controller is further configured tooperate the internal combustion engine based on the stored adjustedvalue of the stored operating parameter reference value.
 17. The systemof claim 15, wherein the selected operating parameter is lever relatedto one of an exhaust gas recirculation fraction or a charge air massflow.
 18. The system of claim 15, wherein the controller is configuredto receive data corresponding to the measured value of the selectedemissions characteristic.
 19. The system of claim 15, wherein theselected emissions characteristic reference value is one of engine outO₂, engine out λ, engine out NO_(x), and intake O₂.
 20. The system ofclaim 15, wherein the controller is further configured to: determine atransient state operating mode adjusting factor based on the operatingpoint; retrieve a stored transient state operating parameter referencevalue associated with a transient state operating mode; and store anadjusted value of the stored transient state operating parameterreference value based on the transient state operating mode adjustmentfactor.
 21. The system of claim 20, wherein the controller is configuredto store an adjusted transient state operating parameter reference valuein a separate adjustable transient state reference table.
 22. The systemof claim 15, wherein the controller is further configured to: comparethe determined adjustment factor value with a predetermined limitingvalue for the requested operating point, and limit the determinedadjustment factor value to a value not exceeding the predeterminedlimiting value.
 23. The system of claim 15, wherein the controller isfurther configured to store an adjusted operating parameter referencevalue in a separate adjustable steady state reference table.